Again, back to basics can be done without being a caster. First you gotta determine throat diameter, even if you adopt the approach by which a bullet just barely fits in a fired case (which will approximate it but still leave you at the mercy of the brass thickness). Armed with that knowledge you can buy bullets larger than that and acquire a simple Lee bullet sizing die (screws into your loading press) and size them to your required diameter. I have no way of knowing if by chance said diameter die exists in their lineup. Your job to play detective there. If the exact diameter die doesn't exist get the one closest and have it reamed/honed to size, or do it yourself- the woods are full of guys who do that themselves. Bottom line is it's easy and cheap.
I can't help but think also those hard-ish bullets you're using can be contributing to your issues. The harder a bullet is the less elasticity it has and the more it resists " bumping up" to seal the bore right from the git-go courtesy of the powder's "explosion". I realize now you're totally at the mercy of commercial casters- wish I had known that- some detective work on your part may turn up a source for something softer. Perhaps even a local caster can accommodate you if you provide a mould and some lead. (A whole lot cheaper than spending $600 on barrel work.)
Soft versus hard is an area that is often counter intuitive to non-veteran cast bullet guys. Often a hard bullet will give more leading and less accuracy than a soft one will. But people insist on hard because that doesn't make sense to them and the commercial caster guys are in the game to make money so that's what they provide.
